The present invention relates to quaternary ammonium compounds useful as fabric softening agents. Such agents are customarily employed in the laundering of fabrics, to impart a feeling of softness and fullness to the fabric, and to reduce the tendency of the fabric to generate static electricity when handled.
Fabric softening agents are often applied to the fabric in the rinse cycle of an automatic clothes washing machine, by adding the agent as part of a pourable liquid or granular solid product. Alternatively, fabric softening agents can be imparted to the fabric in an automatic clothes dryer by placing a thin substrate into the dryer with the fabric, wherein the substrate carries on its surface an effective amount of the fabric softening agent.
The present invention relates more particularly to an improved process in the manufacture of certain quaternary ammonium compounds useful as fabric softening agents. Typically, the manufacture of such agents is a multistep process in which the unquaternized tertiary-substituted amine is prepared, and is then reacted with an appropriate quaternizing agent. The sequence of reactions leading to the formation and recovery of the desired quaternized ammonium compound is notorious for posing problems in obtaining satisfactory yield and conversion rate. The conventional production methods also encounter difficulty in obtaining the desired product with the necessary degree of stability as to the chemical composition, its color and its freedom from unpleasant odor. The existence of such problems is generally believed to be due to the inherently reactive nature of the amine and substituted amine compounds involved, and the relative susceptibility of the reactants employed in the synthesis to undergo competitive side reactions during the synthesis and even following the synthesis leading to the desired end product.
The aforementioned problems are typified in the synthesis of diesterified, dialkylammonium compounds represented by the general formula (1): ##STR1##
In the aforementioned formula (1), the substituents R.sup.a and R.sup.b are saturated or unsaturated alkyl or alkylene, branched or straight chain, radicals containing 12 to 22 carbon atoms, typically derived from fatty acids which are frequently derived from naturally occurring products such as vegetable or animal sources including tallow. Referring again to formula (1), a and b each represent an integer from 1 to 4, R.sup.1 and R.sup.2 each represent alkyl containing 1 to 4 carbon atoms, or other substituents such as benzyl, --CH.sub.2 CH.sub.2 OH or --CH.sub.2 CH(OH)CH.sub.3. The moiety X.sup.- represents an anion. A preferred example of such compounds is the di(acyloxyethyl) dimethylammonium chlorides, which are disclosed for instance in published European patent application No. 88202037.3. However, the conventionally accepted synthetic route for such compounds, as typified by the synthesis disclosed in the aforementioned European patent application, presents operating difficulties and is unfortunately subject to undesired degradation of the desired final product, leading to off-specification properties such as unacceptable color, aroma, and insufficient active ingredient content. That unattractive synthetic process typically reacts bis(hydroxyalkyl) alkyl tertiary amines with two moles of a long-chain acyl chloride. This procedure suffers from the drawbacks that a highly acidic byproduct is generated which imposes exacting and expensive requirements for its safe recovery, and which byproduct also is believed to interfere with the production of the desired end product. Also, it is difficult to prepare the corresponding monoester in a separate step and then to esterify the remaining hydroxyalkyl group in a subsequent step. This procedure adds further to the complexity of the process, with concomitant reduction of yield and risk of generation of undesired contaminating byproducts in the final desired product.
There is thus a need for an improved process for synthesizing compounds of the aforementioned formula (1) which exhibits improved yield of the desired final product and which makes that product available in a form with enhanced stability and improved purity, i.e., freedom from undesired byproducts and their associated undesired properties.